What Does the Updated USDA Zone Map Mean?

You may have heard a rumor about how the USDA has updated the zone map. The rumors are true! In November of 2023, the USDA released an updated hardiness zone map. What are the practical implications of this for you as a farmer or home gardener? In reality, not too much. Here’s a breakdown of how it may affect your farming or gardening practices.

What is a USDA Hardiness Zone?

The USDA hardiness zone map represents key growing information relating to temperature. A hardiness zone generally indicates the average coldest (lowest) winter temperatures for a specific area. The entire continental US, Alaska, Hawaii, and Puerto Rico are divided into 13 numbered zones, indicating how cold that area will likely get each winter. The smaller the number, the lower the average winter low temperature that area experiences. For example, Michigan is a zone 5 or 6, and Florida is generally zone 9 or 10. Those numbered zones are further broken down into sections ‘a’ and ‘b’. The numbers change in increments of 10 degrees Fahrenheit, and the alphabetical sections change in increments of 5 degrees Fahrenheit. For example, zone 7a is, on average, 5 degrees colder in its lowest winter temperatures than zone 7b.

Using the USDA Hardiness Zone Map

Millions of gardeners, farmers, growers, and researchers use the USDA Zone Hardiness map to determine a wide range of factors. The most common use of the map is to decide whether a certain plant can withstand the winters of a particular area. When you go to a garden center, a plant tag, seed packet, or description will state what zones or temperatures that plant is hardy to, meaning where it can be grown. Researchers use it to determine a host of information for farmers and gardeners. Even the USDA Risk Management Agency uses the map to set crop insurance standards and other information. Therefore, it is safe to say that the usage is broad, and the implications of changing such a widely used map are huge.

2023 Map Updates

The biggest takeaway from this update should be that the USDA has gathered a greater quantity of reliable data than was used on the previous 2012 version of the map. The USDA's website states, “The 2023 map incorporates data from 13,412 weather stations compared to the 7,983 that were used for the 2012 map.” In addition, the new map has much higher details of various locations than previously. In the 2012 map, Alaska was broken down into 6-and-a-quarter square mile areas, whereas now, they are down to just one-quarter square mile areas, as shown on the 2023 map.

What Has Changed

The crazy part about implementing these updates into the map is that it resulted in the zones shifting for about half the country. Even in areas where there wasn't a zone shift, the average low temperatures still changed. The USDA explains, “That shift to the next warmer half zone means those areas warmed somewhere in the range of 0-5 degrees Fahrenheit; however, some locations experienced warming in the range of 0-5 degrees Fahrenheit without moving to another half zone.” So, that means most areas of the country are a bit warmer than we originally thought before this new map’s release.

Global Warming?

Obviously, with the warmer shifts in temperature, many people have raised questions about whether this is the government recognizing and conceding to climate change. The USDA has addressed this concern about climate change, “...map developers involved in the project cautioned against attributing temperature updates made to some zones as reliable and accurate indicators of global climate change.” Due to the increase in information and more sophisticated mapping methods, it seems they are implying the map may have been erroneous before and is now more accurate in general.

It is important to recognize that this map is not an end-all-be-all be-all answer to what you can or cannot grow, just like it is not an all-encompassing answer to how our climate continues to evolve. This map is built to only represent average low temperatures. It does not take into account average high temperatures, humidity levels, elevation, variations in terrain, precipitation levels, and snowpack, among other vital factors related to tracking our climate patterns and growing factors. As you continue to practice your craft as a gardener, you will learn more about what your plants need and how you can recognize their responses to local climate and weather changes.

What Zone Am I In?

Anyone can visit the USDA Hardiness Map and input their zip code. This will then tell you what zones you are in, your average annual low temperatures for two different periods of time, and the change in temperature (if any) from the 2012 to 2023 map. This information can be valuable in aiding gardeners and farmers in determining when to plant, what to plant, and how to cultivate their crops. While areas near each other can have different zones due to microclimates. It is always good to check the map if you have questions.

What Should I Do Differently?

I have found that most areas have increased in temperature by about 3 degrees Fahrenheit. That might not be enough to change what you plant each year or even when you plant as compared with previous years but it is important information to keep in mind. I recommend simply taking accurate records from year to year and trying to perceive if your winters or summers truly have warmed enough to change your planting habits. There are microclimates everywhere and even though your area might have shifted zones, that may or may not mean anything for you as an individual gardener. In most cases, this change means you may be able to grow a few more plants than you were able to a decade or two ago.

I live in Michigan, and I have definitely noticed that my winters are not as extreme as they used to be when I was a kid. When the USDA released this new map, and I saw that my area had warmed (according to the map), I was not surprised at all. However, it hasn’t really changed the way I garden. Climate change means many things, not just that temperatures are getting warmer. There is still a risk of frost about as late in the season as there used to be. At least, that is what I have observed.

Care For Our Earth

No matter what, we need to be caring for the earth. Little things we can all do add up tremendously to help our individual ecosystems and, ultimately, the planet. Drive your car less. Plant native species. Opt for second-hand items rather than buying new ones. Use less water. Plant a garden. Grow your own food. Whether or not your zone has changed, we need to do everything we can to preserve our ecosystems and prevent further climate change related to reckless waste and activity.

Lara Wadsworth, True Leaf Market Writer

I am a native of Southwestern Michigan, where I also reside, and I love all things plants! I got a Bachelor's Degree in Horticulture and found the first work-from-home job I could get. Now, I spend my days writing for TLM, playing with my dog, eating delicious food with my husband, and plotting my next landscape or gardening move. I believe everyone should get down and dirty in the soil now and then. Happy Gardening!